I cannot claim authorship for this technique but it creates a lovely pen and wash effect which I wanted to share

Method
Duplicate your photograph (Ctl J)
Use filters-stylise-glowing edges
You want nice sharp, well defined edges so play about until you like the result (I used Edge width 8 Edge Brightness 6 and smoothness 11)
Convert to black and white by your favourite method (you will have white lines on a black bg at this point)
Invert the picture (ctl I) to give you black lines on white.
Create a duplicate of your original photograph and drag it to the top of you layers stack
Use blending modes to create the sort of effect you want (I used multiply)
I then used the eraser to remove some of the top photograph to reveal the lines underneath, making the picture look unfinished.

Hilary this is gorgeous and your result looks like a work of art! Thank you so much for explaining how you did it - I'm copying your words and putting them in my tutorial file!
Lovely work and I really like the addition of the brush and watercolors, too.

Gorgeous, Hilary. I'm going to join Laurie in trying to reproduce this in GIMP. Your technique looks just wonderful. Thanks for sharing your technique. That's a neat building, the dome looks like a government building (ours here in the east tend to look like Greek or Roman temples).

This is wonderful. Thank you for letting us know how you did it. I've got to look through my photos to see if any of suitable for this treatment. Lovely treatment as a sketchbook with the paints and brushes. Well done!